1. Field of the Invention
This invention relates to intravenous solution administering sets for administering infusion solutions such as lactated Ringer's, dextrose, amino acids and hyperalimentation solutions to patients, and in particular to improvements in an inline intravenous final filter unit especially of the bacteria-retentive type adapted to be incorporated in such a set.
2. Description of the Prior Art
At present various infusion solutions are administered to patients for nourishment, adjustment of the electrolyte balance in the body, supplementation of water and therapy. When water or nutriment is parenterally supplemented, the adult requires about 2 l/day of water. This quantity is equivalent to four 500 ml vials. Such large quantities of infusion solutions may be given continually for a prolonged period of time depending on the condition of the patient. These combined quantities will then be 100 l or more. If such a large amount of infusion solution is injected into the body of the patient, very small quantities of fine particles contained in the solution will be accumulated in the body, enhancing the likelihood that the fine particles will cause disorders. In fact, it has been pointed out that fine particles, when introduced into the human body, are liable to cause capillary obstruction, granuloma, damage to cells and necrosis, further aggravating progressive tumor or inducing cancer.
With the development of hyperalimentation solution thereby in recent years, there arises the necessity of using infusion solution administering devices equipped with a final filter unit which is capable of removing bacteria and fungi as well as fine particles by filtration. According to this therapy, an infusion solution incorporating a hypertonic sugar-amino acids mixture, an electrolyte solution and vitamins is administered to the patient at a constant rate over a prolonged period of time through a catheter inserted into the subclavien vein to give the patient the required nourishment, water, etc. solely with the solution. It is therefore critical that the passage for the solution be provided with a final filter unit for removing bacteria and fungi for the prevention of bacterial contamination and candidiasis.
Inline intravenous final filter units are already known in the art. More specifically, Japanese Patent Application Disclosures No. 23286/1973, No. 103890/1975, No. 96089/1975, No. 103487/1974 and No. 1586/1975 disclose such filter units including a cloth bag filter, a filter of fibrous adsorbent coated with a tacky oil and packed into a layer, a filter of randomly arranged material and packed into a layer, a porous metal filter and a filter made from sintered product of fine stainless steel particles, respectively. However, these filter units are all adapted to remove fine particles only from the infusion solution and are unable to remove bacteria.
U.S. Pat. No. 3,471,019 and No. 3,978,857 disclose membrane filter units having a porosity rating of about 0.2 to about 0.5.mu.. Of these units, those having a porosity rating of 0.22.mu., although absolutely bacteria-retentive, do not have a sufficient surface area to provide adequate flow rates with a gravity feed system. Such a filter, if used, necessitates a positive pressure infusion pump to maintain flow rates.